Schedule II - Condensed Financial Information of Registrant - Statement of Operations (Details) - USD ($) $ in Millions	3 Months Ended								12 Months Ended
	Dec. 31, 2023	Sep. 30, 2023	Jun. 30, 2023	Mar. 31, 2023	Dec. 31, 2022	Sep. 30, 2022	Jun. 30, 2022	Mar. 31, 2022	Dec. 31, 2023	Dec. 31, 2022	Dec. 31, 2021
Revenues
Investment income, less investment expense									$ 2,478	$ 2,403	$ 3,293
Net gains (losses) on investments and derivatives									(300)	(1,072)	1,279
Total revenues	$ 14,832	$ 14,497	$ 13,979	$ 13,786	$ 13,648	$ 13,208	$ 12,219	$ 12,336	57,094	51,411	50,601
Expenses
Interest expense									379	335	330
Pension and other postretirement remeasurement (gains) losses									9	116	(644)
Other operating expenses									7,137	7,446	7,260
Total costs and expenses									57,442	53,241	44,135
Income tax (benefit) expense									(135)	(488)	1,292
Net (loss) income attributable to Allstate									(188)	(1,289)	1,614
Preferred stock dividends									128	105	114
Net (loss) income applicable to common shareholders, basic	1,460	(41)	(1,389)	(346)	(303)	(685)	(1,040)	634	(316)	(1,394)	1,500
Net (loss) income applicable to common shareholders, diluted	$ 1,460	$ (41)	$ (1,389)	$ (346)	$ (303)	$ (685)	$ (1,040)	$ 634	(316)	(1,394)	1,500
Other comprehensive income (loss), after-tax
Unrealized net capital gains and losses									1,651	(2,853)	(2,583)
Unrealized foreign currency translation adjustments									67	(150)	(8)
Unamortized pension and other postretirement prior service credit									(16)	(43)	(59)
Discount rate for reserve for future policy benefits									(10)	228	49
Comprehensive income (loss) attributable to Allstate									1,494	(4,087)	(984)
Allstate Corporation
Revenues
Investment income, less investment expense									45	59	13
Net gains (losses) on investments and derivatives									(28)	(34)	12
Total revenues									17	25	25
Expenses
Interest expense									396	351	328
Pension and other postretirement remeasurement (gains) losses									12	179	(611)
Pension and other postretirement (benefit) expense									55	(98)	(218)
Other operating expenses									142	56	71
Total costs and expenses									605	488	(430)
(Loss) gain from operations before income tax benefit and equity in net income of subsidiaries									(588)	(463)	455
Income tax (benefit) expense									(143)	(103)	93
(Loss) gain before equity in net income of subsidiaries									(445)	(360)	362
Equity in net income (loss) of subsidiaries									257	(929)	1,252
Net (loss) income attributable to Allstate									(188)	(1,289)	1,614
Preferred stock dividends									128	105	114
Net (loss) income applicable to common shareholders, basic									(316)	(1,394)	1,500
Net (loss) income applicable to common shareholders, diluted									(316)	(1,394)	1,500
Other comprehensive income (loss), after-tax
Unrealized net capital gains and losses									1,651	(2,853)	(2,583)
Unrealized foreign currency translation adjustments									67	(150)	(8)
Unamortized pension and other postretirement prior service credit									(16)	(43)	(59)
Discount rate for reserve for future policy benefits									(10)	228	49
Other comprehensive income (loss), after-tax									1,692	(2,818)	(2,601)
Comprehensive income (loss) attributable to Allstate									$ 1,504	$ (4,107)	$ (987)